It’s a rare consideration for President Donald Trump, who has boasted of a new foreign policy formed around the idea of strength and unabashedly putting his nation’s interests first. But his No. 2 billing will be the tradition he must respect when leaders deliver their messages to the world at the U.N. General Assembly on Tuesday.

Brazil has opened the annual gathering of presidents and prime ministers, popes and premiers, and kings and chancellors for more than six decades, with rare exceptions. The U.S. leader has had to wait his turn.

Anticipation for Tuesday’s set of speeches is high. Trump will be making his debut at the annual ministerial meeting of the U.N.’s 193 member nations, hoping to sell a vision of international co-operation defined less by collective obligation and more by sovereign states taking voluntary initiatives. His counterparts from around the globe will be closely gauging how much Trump tailors his message for the most prominent audience in international diplomacy.

The origins of the tradition-bound United Nations’ lineup are somewhat murky.

In 1947, top Brazilian diplomat Oswaldo Aranha presided over the General Assembly session that led to the U.N.’s plan for the partition of Palestine into two states, one Jewish and one Arab. Civil war meant the plan was never implemented, despite the world body’s 33-13 vote in favour.

But Brazil’s historic role is recognized to this day. It led off the General Assembly from 1949 to 1951, before Cuba, the United States and Canada all got top-of-the-billing turns. And since 1955, Brazil almost always has spoken first. The U.S., as the United Nations host country, has gone second.

The tradition hasn’t always been followed. In 1976, Chad took America’s place when President Gerald Ford was late.

Then in 1983 and 1984, Brazil and the U.S. flipped positions, allowing President Ronald Reagan to kick off the proceedings.

As U.N. spokesman Stephane Dujarric said Monday: “There are many unexplained traditions at the U.N. and this is one of them.”